Field of the Invention
The present invention relates to a thermal processing method of heating a thin-plate fine electronic substrate (hereinafter simply referred to as a “substrate”) such as a semiconductor wafer to which impurities are introduced, by irradiating the substrate with light.
Description of the Background Art
In a process of manufacturing a semiconductor device, impurity introduction is a process necessary for forming a p-n junction in a semiconductor wafer. Currently, a typical impurity introduction is achieved by an ion implantation technique and a subsequent annealing technique. The ion implantation technique is a technology in which impurity elements such as boron (B), arsenic (As), and phosphorus (P) are ionized to collide onto a semiconductor wafer with a high acceleration voltage and physically perform impurity implantation. Implanted impurities are activated through anneal processing. In this process, an annealing time of several seconds or longer allows the implanted impurities to deeply diffuse by heat to have a junction depth much larger than required, potentially causing difficulties in favorable device formation.
For this reason, flash lamp annealing (FLA) has attracted attention recently as an anneal technology of heating a semiconductor wafer in an extremely short time. The flash lamp annealing is a thermal processing technology of rising temperature only at the surface of a semiconductor wafer in which impurities are implanted, in an extremely short time (several milliseconds or less) by irradiating the surface of the semiconductor wafer with flash light using a xenon flash lamp (hereinafter, a simple notation of “flash lamp” means the xenon flash lamp).
The xenon flash lamp has an emission spectral distribution ranging from ultraviolet to near-infrared, and has a wavelength shorter than that of the conventional halogen lamp, which is substantially the same as the fundamental absorption band of a silicon semiconductor wafer. Thus, when the semiconductor wafer is irradiated with flash light from the xenon flash lamp, less light is transmitted and thus the temperature of the semiconductor wafer can be rapidly risen. It has been found that the flash light irradiation in an extremely short time less than several milliseconds can selectively rise temperature only at the vicinity of the surface of the semiconductor wafer. Thus, when the xenon flash lamp is used to rise temperature in an extremely short time, only impurity activation can be executed without diffusing impurities deeply.
Japanese Patent Laid-Open No. 2013-201453 discloses that an insulated gate bipolar transistor (IGBT) is used to adjust the emission output waveform of a flash lamp by controlling current flowing through the flash lamp, and maintain the surface temperature of a semiconductor wafer at a target temperature for 10 milliseconds approximately. When the surface temperature of a semiconductor wafer is maintained at a target temperature for several milliseconds to several tens of milliseconds, repair of any defect introduced to the semiconductor wafer during impurity implantation can be performed in addition to the impurity activation.
The most useful technological characteristic provided by a flash lamp is an extremely short emission time, and thus the flash lamp annealing can execute only the impurity activation but not the impurities diffusion. Recently, the performance of a semiconductor device such as a CMOS has been required to be further enhanced by optimizing the overlapping length of source-drain extension under a gate, which requires appropriate control of the impurity diffusion. However, the conventional flash lamp annealing is basically intended to reduce the impurity diffusion to the extent possible, but cannot control the impurity diffusion.